Wave movements in the sea and in large inland lakes constitute a potential source of energy that has scarcely been exploited so far. However various suggestions have been made to use the vertical movements of the sea for producing electrical power in a generator. Since a point on the sea surface makes a reciprocating vertical movement it is suitable to use a linear generator to produce the electric power.
WO 03/058055 discloses such a wave power unit where the moving part of the generator, i.e. the part that corresponds to the rotor in a rotating generator and in the present application called translator, reciprocates in relation to the stator of the generator. In that disclosure the stator is anchored in the sea bed. The translator is by a wire, cable or a chain connected to a body floating on the sea.
For a wave power unit of this kind it is important to optimize the amount of the wave energy that is absorbed by the wave power unit and supplied as electric energy. This includes considerations relating to the mechanical as well as the electrical aspects of the system. The amount of power absorbed by the wave power unit is dependent on the hydrodynamic parameters and damping factors of the energy system. The floating body determines the hydrodynamic parameters and the load, together with the generator and the sea cable generates the damping factors.
A high power capture ratio, defined as the quotient between the extracted power divided by the power incident on the cross section of the floating body, is achieved when the natural frequency of the wave power unit coincides with the wave frequency. Therefore it is desirable to reach a design of the wave power unit that results in such mechanical resonance. However the various parameters that have to be considered and various other requirements that the system has to meet renders it very complicated to optimize the power capture ratio by the design of the mechanical components of the system.
The present invention is focused on the electrical components of the system. It is well known that electrical resonance in an electrical circuit involving capacitors and inductors can create high voltages and high power, so-called reactive power. However, since this can cause damage both to traditional generators and other electric power components, electrical resonance is generally avoided in electrical systems and networks. Hence, there lies a great potential for improved power conversion in overcoming the detrimental effects of electrical resonance in an electrical circuit. The object of the invention thereby is to increase the power capture ratio of an electric device which may be used as a wave power unit to produce electric energy.